To catch up on the plots, there are websites out there with story recaps. That's how I caught up after missing the entire first season.
Sydney is the messenger; her sister is the PASSENGER. She was injected with the Rimbaldi serum as a child and retained the entire "message" in her memory as a result. Sloan used the Rimbaldi fluid to extract the message stored in her memory. He wanted to do it slowly so as to avoid overtaxing her brain and perhaps killing her, but then Lauren and Sark showed up and demanded he give her a huge dose quickly and if she dies, so be it. Sloan called in two goons, claimed he'd made an error and tried to save Nadia but Sark and Lauren shot the goons. At that point Sydney and Vaughn charged in, Sydney rescued Nadia while Vaughn chased Sark and Lauren, unsuccessfully. Sloan escaped, and Nadia told Sydney and Vaughn that he tried to protect her.
Irina had an affair with Sloan, which resulted in Nadia's birth.
Meanwhile, Syd's dad (Jack) is getting it on with Irina's sister, Isabella Rosellini. I really miss Lena Olin and wish she would return to the series.
Lauren and her mother are part of the covenant, and they killed Lauren's dad (a U.S. Senator) when he caught on to their treachery. They then planted evidence to make it look like HE was the traitor, but Jack and Vaughn figured it out, which is why Lauren tried to kill Vaughn.
